This invention relates to solid air freshener compositions. More particularly, this invention relates to a solid air freshener gel composition utilizing a cross-linked carboxymethyl cellulose as the primary gelling agent.
During recent years, a number of solid air freshener compositions have been marketed with a reasonable degree of success. These compositions, which are primarily based on carrageenan, release perfume or freshening agent continuously over a period of time. Although carrageenan adequately forms gels and is capable of entrapping perfumes for slow release, the physical properties of the carregeenan gel create a number of problems which must be closely watched during production and formulation. One of the most important problems regarding carregeenan is a problem known as syneresis, i.e., the loss of moisture from the gel to the surface which gives the gel a wet appearance and can create difficulties. The syneresis problem can be alleviated in carrageenan gels by using sufficiently high percentages of the carregeenan gelling agent. However, carregeenan is an expensive material and it is very difficult to produce an economic solid air freshener gel without having significant amounts of syneresis.
Attempts have been made to alleviate this syneresis problem by incorporating various additional metal ions, such as potassium ions, into the composition. Also, attempts have been made to increase the stability of these materials and decrease syneresis by adding other thickeners, such a guar gum and gelatin, to the system. An example of compositions of the above type are U.S. Pat. 2,927,055 and British Patent 1,241,914. However, compositions within the scope of the above patents tend to produce some degree of syneresis depending upon the amount of carrageenan utilized and, accordingly, a satisfactory gel is difficult and expensive to produce.
In addition to the syneresis problem, the prior art carrageenan systems are difficult to produce in large volumes. These systems are heat sensitive gels and, accordingly, production requires both heating and cooling means for proper mixing and processing. These heating and cooling means add significantly to the costs of these prior art systems and further require careful monitoring of the process.
It has been discovered that a known characteristic of carboxymethyl cellulose, i.e., when certain trivalent metal cations are added to CMC they will cross-link the carboxymethyl cellulose to form a gel, can be used to form an effective, inexpensive air freshener gel. Examples of disclosures relating to CMC gels are U.S. Pat. 3,749,174, which discloses the utilization of sodium carboxymethyl cellulose and chrome potassium sulfate gels in drilling muds, British Patent 1,163,518, which discloses a method of laying pipe which includes filling the trench with an aqueous carboxymethyl cellulose solution loaded with sand and including aluminum sulfate, "Industries Gums" by J. W. BeMiller, Academic Press, New York, 1973, pp. 716-7, and a publication of Hercules Chemical entitled "Cellulose Gum-Sodium Carboxymethyl cellulose" copyrighted 1971.